Incinerator draft system

ABSTRACT

A draft system for controlling the combustion air entering and exhaust exiting &#39;&#39;&#39;&#39;teepee&#39;&#39;&#39;&#39;wood waste burners is presented. The system includes forced underfire air, forced overfire air, tangential overfire vents, a top damper, and controllers therefor, operable responsive to the internal temperature of the burner. The controllers maintain the burner temperature at preferably between about 800-900 degrees Fahrenheit for complete combustion of wood waste fuel by controlling the rate of forced underfire and overfire air, venting into the burner, and by controlling the damper. In a preferred embodiment a first controller is operably coupled to the underfire air system, the overfire air system, and the cooling vents while a second controller is operably coupled to the damper. The system also includes alternate manual controls and a strip chart recording pyrometer.

United States Patent [191 Stearns INCINERATOR DRAFT SYSTEM George H. Stearns, Kalispell, Mont.

[73] Assignee: Rolies Maschineworks, Inc.,

Kalispell, Mont.

[22] Filed: Apr. 30, 1973 [21] Appl. No.: 355,467

Related US. Application Data [63] Continuation-in-part of Ser. No. 159,257, July 2,

197], Pat. NO. 3,730,113.

[75] Inventor:

[111 3,807,325 [451 Apr. 30, 1974 Primary ExaminerKenneth W. Sprague Assistant Examiner-Larry l. Schwartz Attorney, Agent, or Firm-LeBlanc & Shur [5 7] ABSTRACT A draft system for controlling the combustion air entering and exhaust exiting teepeewood waste burners is presented. The system includes forced underfire air, forced overfire air, tangential overfire vents, a top damper, and controllers therefor, operable responsive to the internal temperature of the burner. The controllers maintain the burner temperature at preferably between about 800-900 degrees Fahrenheit for complete combustion of wood waste fuel by controlling the rate of forced underfire and overfire air, venting into the burner, and by controlling the damper. In a preferred embodiment a first controller is operably coupled to the underfire air system, the overfire air system, and the cooling vents while a second controller is operably coupled to the damper. The system also includes alternate manual controls and a strip chart recording pyrometer.

10 Claims, 7 Drawing Figures PATENTEWNOIQM 3.801325 SHEET 2 BF 4 PATENTEBAPRBUIHM -3;807;325 4 SHEET 3 BF 4 OVERFIRE VENT ACTUATOR OVERFT RE VENT ACTUATOR TOP DAMPER WINCH WINCH MOTOR MOTOR BLOWER SHUTTER PHTE-mmo m4 325 SHEET l 0F 4 1:: 1:! l: :5 04 1 l i R [m l l i I f" H i 86 1 00 1 AUTO MAN 1 OFF ON J H CONTROLLER OFF SELECTOR l POWER RECORDER 90 POWER 0 88 88 ON OFF 92 94 96 98 g ON 'ON- OPEN OPEN OPEN OPEN OFF OFF CLOSED CLOSED CLOSED CLOSED :E UFB UFB OFB TOP UFB OFB OF POWER POWER POWER DAMPER SHUTTER SHUTTER VENTS ,1 i I j i g5 l 1 l N J! W i Y r EH11 R INCINERATOR DRAFT SYSTEM This application is a continuation-impart of my copending US. Pat. application Ser. No. 159,257 filed July 2, 1971 now US. Pat. No. 3,730,113.

This invention relates to a draft system for an incinerator, and in particular to a thermostatically controlled draft system for maintaining an incinerator at an optimum temperature for complete combustion of the materials therein. The system of this invention is specially adapted for use with modern sawmill teepee" wood waste burners to facilitate efficient combustion of waste woody materials and to minimize the pollutants emitted therefrom.

Specifically, the system of this invention is an improved version of the draft system described in my aforementioned patent application. Accordingly, the disclosure of my U.S. Pat. application Ser. No. 159,207, filed July 2, 1971, is hereby incorporated by reference.

Bark, sawdust, and other sawmill wastes are normally disposed of in an incinerator structure called a teepee burner. These installations have generally a truncated, conical shape similar to an Indian teepee, and typically have a floor diameter of from 40 to 60 feet. The standard burner, however, has a burner floor either forty or 50 feet in diameter. Waste material is dumped into the burner through the top thereof, from a conveyor which may terminate to feet above the burner floor. The walls of the installations are normally constructed of large metal plates disposed in concentric rings about a supporting frame.

Prior burners have utilized a single source of forced air with one or more outlets in the burner floor to promote combustion of waste materials, In addition, vents which may be thermostatically controlled have been used in the sides of the burners to promote circular convection currents. These prior burner installations, however, have a common deficiency. Waste materials normally are consumed at a very high temperature only in the center of the underfire draft outlet, and materials remote from the outlet or grate merely smolder and arev incompletely consumed, Solid combustion products and ash emitted after incomplete combustion in these installations are an unacceptably high source of air pollutants.

Overfire forced air or vents in an incinerator theoretically should facilitate more complete combustion. However, without an efficient underfire draft, and a balance between the underfire and overfire, forced draft and venting, the overfire draft merely compounds the problem by providing a cyclonic circulation within the burner to entrain partially consumed particles in the smoke emitted therefrom.

The problem of incomplete combustion may be solved in part by my aforementioned prior invention which provides an efficient underfire draft, as will be subsequently explained.

Ideally fuel from the conveyor should accumulate in the center of the burner floor. However, when the fuel is dropped from a conveyor 20 to 30 feet above the burner floor, it tends to scatter and accumulate at peripheral areas remote from conventional centrally located underfire draft outlets. In order to provide a better underfire draft prior installations have utilized a plurality of draft outletsspaced around the burner floor. These outlets are fed, normally, by a common source of forced air.

Therefore, if one or more of the draft outlets are covered by fuel the flow of air through the remaining outlets increases, promoting uneven burning at undesirably high temperatures. In some systems if an inlet becomes plugged the tlow to downstream inlets is stopped which also promotes uneven burning.

However, in my aforementioned patent application an efficient underfire draft was provided by a plurality of independently controlled sources of upwardly directed, forced air in the burner floor. Mutually spaced grates are disposed in a symmetrical array around the center of the dropping area for the fuel conveyor. More complete, controlled combustion throughout the burner installation is thereby provided because each grate is fed by a separate forced air conduit. If one grate becomes plugged, air will thereby not be forced into the remaining grates at an increased rate.

The system described in my aforementioned application also provided an overfire draft to create a cyclonic circulating system within the incinerator. The overfire draft disclosed therein included mutually spaced vents disposed in the incinerator walls, surrounding the burner floor, and tangentially directed blowers having outlets extending into the incinerator.

However, it has now been discovered that by providing a controlled draft system according to the instant invention efficient combustion will be insured because the burner may be maintained at an optimum combustion temperature. Forced underfire and overfire air, venting and a damper, are utilized to control and maintain the desired temperature.

The draft system of this invention includes the forced underfire system described in my aforementioned application which utilizes blowers which communicate with individual grate boxes through separate rectangular tubes. Each blower is equipped with motorized shutters to control the air volume entering the tubes. In addition, each tube has a damper which can restrict air to any particular grate box. Therefore, air to any grate box not covered by fuel may be closed off to avoid burning at undesirably high temperatures.

The system of this invention also includes a forced overfire system. consisting of blowers supplying metered air through motorized shutters on each blower intake. The blowers are disposed above the burner floor and are tangentially directed to aid in the internal air turbulance within the burner.

lnaddition, the system of this invention includes tan gential overfire vents which are designed to introduce fresh air into the burner. The vents are mechanically linked around the burner, and are operated by linear actuators designed to open and close the vents as desired to admit cooling air into the burner.

Finally, a downwardly opening damper is also provided in the top of the burner to restrict the escaping gases, and therefore raise and lower the internal temperature of the burner as desired. The damper comprises opposed doors which are operated by motorized, electric winches.

An automatic control system is provided for the underfire and overfire blowers, the vents, and for the damper. The control system operates responsive to thermocouple probes disposed within the burner to maintain the interior thereof at, for example, a desired temperature of between about 800 and 900 Fahrenheit.

To operate the system of this invention, when the burner is first lighted the top damper will be in a closed position, the overfire tangential vents will be closed, and the under and overfire blower shutters will be slightly open. As the temperature begins to rise the top damper will begin to open. As the burner becomes still hotter the underfire and overfire blower shutters will activate to supply more air for combustion, and as the burner reaches the top set limit, the tangential air vents will open affording cooling. The burner top damper will open fully and the underfire and overfire shutters will close. When the temperature begins to drop the aforementioned steps will be reversed so that the burner may be maintained within a desired combustion temperature range.

Accordingly, it is an object of this invention to provide an improved, controlled draft system for incinerators.

It is another object of this invention to provide a draft system for an incinerator including a plurality of separately controlled, symmetrically arranged, forced underfire and overfire air outlets and vents opening into the incinerator to provide an upwardly directed, circulating draft throughout the incinerator for uniform and complete combustion of waste materials.

It is another object of this invention to provide a draft system for an incinerator including a controlled damper at the top thereof for controlling the temperature within the burner.

It is yet another object of this invention to provide a draft system for an incinerator including forced underfire air, forced overfire air, vents disposed in the sides thereof, a controlled damper at the top thereof, and controllers for maintaining a controlled rate of air entering the incinerator and exhaust gases exiting therefrom.

It is still another object of this invention to provide an underfire and an overfire draft for an incinerator including a plurality of grates mutually spaced in the burner floor, each grate having a separately controlled source of underfire forced air, and tangential blowers extending through the sides of the incinerator structure for providing separately controlled sources of forced overfire air.

It is still another object of this invention to provide a draft system for incinerator structures including tangential vents disposed in the sides thereof, said vents having a common control whereby said vents may be opened or closed responsive to the internal temperature within said incinerator.

It is yet another object of this invention to provide a draft system for a waste incinerator adapted to completely combust wood and waste materials whether in the form of sawdust, chips, or large pieces of bark or wood utilizing a plurality of separately controlled draft boxes disposed in the floor of said incinerator as an underfire air system, a plurality of tangentially directed blowers disposed in the wall of said structure for providing an overfire draft system, a plurality of vents mutually spaced around the walls of said structure said vents being commonly controlled for selectively admitting a predetermined rate of cooling air for the interior of said incinerator, and a damper at the top thereof; said system being controlled by potentiometric controllers responsive to the temperature within said incinerator for maintaining the combustion temperature therein in an optimum range for complete combustion of waste materials.

. These and other objects will become readily apparent with reference to the drawings and following description wherein:

FIG. 1 is a plan view of a burner installation utilizing the draft system of this invention, the upper portion of the incinerator being removed to expose the burner floor;

FIG. 2 is a fragmentary top view in partial section illustrating the actuating mechanism for the vents;

FIG. 3 is a top view of the exhaust outlet for the burner installation illustrating the damper of this invention;

FIG. 4 is a fragmentary view in partial section of the burner top;

FIG. 5 is a fragmentary plan view of the burner installation of FIG. 1 in partial section;

FIG. 6 is a block diagram flow sheet illustrating the controller operation of this invention; and

FIG. 7 is a plan view of the layout of the control panel for the burner installation of this invention.

With attention to the drawings, FIGS. 1 and 5 illustrate the lower portion of a conventional teepee burner, adapted to include the controlled draft system of this invention. The incinerator 10 is typically constructed in concentric rings 12 of metal plates 14 on a supporting frame (not shown). The structure is generally in the shape of a trucated cone and typically has a base diameter of 40, 50, or 60 feet.

Fuel enters the incinerator 10 from an overhead conveyor (not shown). Fuel drops from the conveyor to the incinerator floor 18, normally a distance of 20 to 30 feet. Because the orientation of the conveyor in relation to the incinerator 10 may vary from structure to structure, it is necessary through trial and error to define an approximate center of the drop zone 20 on floor 18. Center 20 often does not coincide with the center of floor l8.

Underfire air for the draft system of this invention is furnished through separately controlled inlets 22 mutually spaced in a symmetric array on the floor 18 of incinerator 10. The inlets surround the center of the drop zone 20. Inlets 22 are preferably draft boxes 24 as shown in FIG. 5, which support cast iron grates 26. The grates 26 may be of any conventional design.

As shown in FIG. 5 draft boxes 24 are preferably mounted below the floor 18 of incinerator 10 so that the grates 26 lie in a horizontal plane therewith. FIG. 1 illustrates a preferred array of inlets 22 when the floor 18 has a diameter of 40 or 50 feet, but as discussed in my aforementioned parent application, if the burner floor is larger than 50 feet in diameter the inlets will be mutually spaced in a slightly different array.

The preferred array of inlets 22 may be described as an outer grouping of draft boxes 24 and an inner grouping of draft boxes 24' about center 20. In FIG. 5 four draft boxes make up each grouping. The vertical axis of each draft box 24 in the inner grouping is spaced an equal distance from the center 20 and from the vertical axes of adjacent boxes. For example, in FIG. 5 the vertical axis of each draft box 24' in the inner grouping is preferably 4 feet from the center of the drop zone 20. A circle having a radius of 4 feet drawn about center 20 will pass through each of the vertical axes of the draft boxes 24 at intervals. It should be noted that the longitudinal axis of each grate 26 need not pass through center 20.

The grate boxes 24 in the outer grouping are merely symmetrically disposed about the center 20, and the vertical axis of each draft box 24 need not be spaced an equal distance from the vertical axes of adjacent boxes 24.

In the preferred embodiment of FIG. 1 the vertical axis of each draft box 24 in the outer grouping is a corner of a rectangle having the center of the drop zone as its center. In addition, a diagonal of this rectangle should coincide with the centerline of the conveyor (not shown). If the conveyor is aligned with the diagonal of the array of draft boxes 24 and 24 the likelihood that fuel will scatter beyond the periphery of the outer grouping will be minimized.

In the incinerator of FIG. 1 having a floor diameter of 40 to 50 feet, the distance a is preferred to be about 13 feet, b about fourteen feet and 0 about 8 feet.

It should be emphasized that the draft boxes may be arrayed in any desired configuration over the anticipated drop zone, and this invention is not intended to be limited to the specific number of draft boxes described in the preferred embodiment or to the array shown in FIGS. 1 and 5. As will be obvious to those skilled in the art, a plurality of mutually spaced draft boxes may be disposed in any desired symmetrical array within the scope of this invention.

Forced air is admitted through each draft box 24 by conduits 30. Each conduit 30 connects the draft box 24 and a conventional blower 32. Admission of air into each conduit 30 may be controlled by a manually operated damper 34. Conduits 30 preferably are 6 inches X 8 inches in cross-sectional area.

As shown in FIGS. 1 and 5, each blower 32 feeds four conduits 30 and four draft boxes 24. The blowers 32 are of conventional paddle-wheel design and preferably are driven by motors having a HR 1,800 r.p.m. capacity. Each blower 32 is equipped with shutters 36. Shutters 36 control the air inlet to the blower 32, and are preferably motorized so that they may be opened or closed merely by energizing a motor (not shown).

Forced air from blowers 32 enter each of the four associated conduits whether the grate 26 at the respective draft box 24 is covered by waste materials or not. But, if desired, the combustion area within the burner 10 may be restricted by closing selected dampers 34 to block admission of forced air to the draft boxes 24 connected thereto.

The number of blowers 32 directing forced air into the draft boxes 24 will depend upon the underfire draft desired. While one blower supplies four draft boxes in the preferred embodiment, it will be obvious to those skilled in the art that more blowers could be provided for a smaller number of draft boxes.

Forced overfire air for the draft system of this invention is furnished by tangentially directed blowers 37 which are preferably mounted in the sides of incinerator 10. Two blowers 37 are equidistantly spaced, in the preferred embodiment of this invention, around the exterior of the burner 10. As will be obvious to those skilled in the art two or more blowers 37 may be provided within the scope of this invention, if desired. Each blower 37 has shutters 38 at the air inlet. Shutters 38 are controlled by an electric motor (not shown) so that the shutters may be opened and closed by energiz- .ing the motor. In this way, the flow of air through the blowers 37 may be increased or decreased as desired.

Tangentially directed overfire vents 40 are spaced equidistantly around the sides of incinerator 10 as shown in FIGS. 1 and 5. The vents 40 are preferably 30 inches long by about 12 inches deep and are horizontally mounted, l per panel 14 at a angle to the panel. With attention to FIG. 2, each vent 40 is provided with a damper 42 which may be manually operated, if desired, but in the preferred embodiment of this invention, is motorized. The vents 40 are mechanically linked half-way around the burner in each direction by rods 44, which rods are interconnected with damper 42 by a linkage 46 and 46. Twin linear actuators 48 and 48 are connected to the first adjacent link mechanism 46 and 46' by push rods 50 and 50'. Actuators 48 and 48' are protected from the heat of the burner 10 by a heat barrier 52. Link mechanism 46 and 46 shown in FIGS. 2 and 5 has been deleted'from FIG. 1 in the interest of clarity.

Accordingly, when actuators 48 and 48 are actuated for a linear stroke in opposite directions, the mechanically linked dampers 42 will be either opened or closed depending upon the direction of the stroke.

It will be obvious to those skilled in the art that the size of the vent openings will depend upon the size of the burner. In addition, any conventional linking mechanism may be provided for opening and closing the dampers 42 simultaneously around the installation 10. Each vent is normally disposed, however, about 4 feet above the level of the burner floor.

With attention to FIGS. 3 and 4, the walls 14 of burner installation 10 terminate in an exhaust outlet 54 which may be covered in a conventional manner by a screen 56. A damper mechanism according to this invention is provided in exhaust outlet 54. The mechanism includes a truss 58 which may be constructed of square tubing, and is disposed horizontally across the opening 54. Twin opposed damper doors 60 are hingedly attached to truss 58, and normally open downwardly, as shown in FIG. 4. Cables 62, attached to doors 60, extend over pulleys 64 to twin electric winches (not shown).

Accordingly, actuation of the winches will either open or close doors 60, and in the event the winches fail, the doors will open downwardly to'the full open position so that the burner cannot overheat. The doors may be fabricated from square tubing with a steel skin, and the damper mechanism is designed to allow complete closure of the burner top, as desired, when lip 64 on doors 60 abuts the lower edge 66 of opening 54.

In addition to functioning as forced air inlets, draft boxes 24 may also be utilized to initially ignite the fuel to be incinerated. As shown in FIG. 1, a pair of draft boxes 24 in the inner grouping may be connected by an underground pipe 70 to a source of flammable gas such as tank 72 remote from the incinerator installation. Tank 72 preferably contains propane under pressure.

To begin incineration wood, paper or other dry flammable material is placed on grate 26 and ignited. Valve 74 is then opened admitting gas through pipe 70 to nozzles (not shown) located immediately below grates 26. The draft system of this invention, as will be subsequently explained, is then actuated so that when waste material fed to the incinerator 10 by the conveyor (not shown), and is burning satisfactorily, valve 74 may be closed to allow incineration to proceed until completed.

With attention to FIGS. 6 and 7, the control system for the motorized shutters 36 on the underfire air, the motorized shutters 38 on the overfire air, the linear actuators 48 and 48 on the vents, and the electric winches for the damper 60 is provided preferably by two potentiometric controllers. Preferably two thermocouple probes 76, as shown in FIG. I, extend into the burner to monitor the temperature therein. Thermocouple probes may have a length of approximately 10 feet such as the type J thermocouple furnished by Heat Technology Corporation. This thermocouple probe has a length of 10 feet with 8 gauge iron-constantan with a 304 stainless steel protection tube.

Potentiometric controllers utilized in the preferred embodiment of this invention are for example Ser. 100 Model 135 Type-J controllers having a range of to l,500 degrees Fahrenheit obtainable from Syscon International, Inc. of Southbend, Ind.

With attention to FIG. 6, in the preferred embodiment of this invention one thermocouple probe 76 is coupled to a strip chart recorder. The strip chart recorder provides heat information for manual operation of the system should the automatic controller malfunction, and in addition, provides a record of the burner operating temperatures for state inspection. An exemplary chart recorder is that furnished by Esterline Angus of Indianapolis, Ind. This chart recorder has a range of 0 to 1,200, a chart speed of about 1 inch per hour, and is motor operated by a 120 volt, 60 Hz, 2 rpm. motor.

The second thermocouple probe 76 is operably coupled to two potentiometric controllers 78 and 78. Controller 78 is operably coupled to each of the two top damper winch motors 80 for opening and closing the damper as required. Controller 78 operates the overfire blower shutters 38, the underfire blower shutters 36, and the vent actuators 48 and 48.

Operation of the control system for the device of this invention may be seen with reference to the control panel of FIG. 7. Control panel 82 mounts potentiometric controllers 78 and 78' and strip chart recorder 77. The panel contains a master on-off switch 84 and an automatic-manual selector switch 86. in addition, the panel also contains on-off power switches 88 for the underfire blowers, 90 for the overfire blowers, 92 for the damper, 94 for the underfire blower shutters, 96 for the overfire blower shutters, and 98 for the vents.

An on-off switch 100 is also provided for the recorder, and a second switch 102 is provided for the controllers.

Accordingly, when the master power switch 84 is on, and selector 86 is selecting automatic operation, and the remaining switches 88, 90, 92, 94, 96, 98, 100, and 102 are on, the control system of this invention will operate as follows:

After the burner has been lighted as described above, the top damper 60 will be in a closed position, the dampers 42 and vents 40 will be closed, and the underfire and overfire blower shutters 36 and 38 respectively will be open slightly. As the temperature within the burner begins to rise, the top damper 60 which is separately controlled, will begin'to open. As the temperature further increases, the underfire and overfire blower shutters 36 and 38 will activate supplying more air for combustion. Finally, as the burner reaches its top set point limit as set by the indicators 104 on controller 78 and 78', the dampers 42 on the tangential air vents 40 will open to afford cooling. The burner top door will then be in its fully open position and the blower shutters 36 and 38 will begin to close. As the temperature starts to drop, the process is reversed thereby holding a set temperature preferably of between 800 and 900 Fahrenheit within the burner installation.

in summary, to eliminate the problem of incomplete combustion which leads to excessive emissions of solid and ash in incinerators, a controlled draft system has been described. The draft system of this invention includes a plurality of mutually spaced separately controlled draft inlets mounted in the burner floor and arrayed about the center of the fuel drop zone. Each of the draft inlets in the array communicates with forced air source such'as a conventional blower. The system of this invention also includes overfire air supplied by a plurality of tangentially directed blowers mutually spaced around the installation and extending through the side thereof. Cooling for the system is provided by tangentially directed vents mutually spaced at equal distances around the burner floor. The vents are interconnected by mechanical linkages so that they may be opened and closed simultaneously, as desired. Finally, the system includes a damper at the exhaust outlet in the top of the installation. The damper, vents, and underfire and overfire air are controlled through a plurality of potentiometric controllers operating responsive to thermocouple temperature probes extending into the burner. In the alternative, the control system provides for manual operation as desired, and in addition, a strip chart recorder is provided for recording the operating temperatures of the installation.

It will be obvious to those skilled in the art that if desired, other types of controllers may be utilized for providing proportionate control of each system variable, or, for providing merely on-off control within a combustion temperature range. This invention is not intended to be limited to the particular type of controller, or to the means for actuating the vents, damper or blower shutters. This invention is also not intended to be limited to the specific type of display board provided wherein manually operable controls are provided in the event it is desired to operate the installation without the aid of the controllers.

The invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The present embodiment is therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.

What is claimed and desired to be secured by United States Letters Patent is:

1. An improved draft system for an incinerator structure having a burner floor, walls extending upwardly therefrom, an exhaust outlet in the upper portion thereof, and fuel supply means including a conveyor extending through a port in the upper portion of said incinerator walls and terminating over said floor, said conveyor adapted to drop fuel in a preselected zone on said floor, said structure comprising:

a plurality of mutually spaced underfire draft boxes,

each of said boxes mounted in the floor of said incinerator, the upper surface of each box forming a grate, said draft boxes being spaced in a predetermined configuration about the conveyor drop zone;

plurality of underfire blowers mounted externally to said incinerator, and separate conduits interconnecting said draft boxes and said blowers, each of said draft boxes separately communicating with the outlet of one of said blowers through one of said conduits;

a damper disposed within each of said conduits adjacent said blowers, said dampers adapted to separately control the flow of air from each of said blowers to each of said draft boxes;

a plurality of overfire air blowers mounted on the exterior of said structure with outlets extending through the side walls thereof, said blower outlets being tangentially and horizontally directed into the interior of said structure to provide a cyclonic circulation of air currents within said structure;

a plurality of mutually spaced vents extending through the walls of said incinerator each of said vents having a damper therein;

damper means disposed in the exhaust outlet of said structure for restricting the passage of exhaust gases therethrough;

temperature responsive control means operably coupled to said underfire and overfire air blowers, to each vent damper and to said exhaust damper means for permitting only a preselected flow of air into said structure and of exhaust gases from said structure so that when woody materials are consumed in said incinerator structure, the combustion temperature thereof may be maintained within a predetermined range for complete combustion.

2. The system of claim 1 further comprising first temperature sensing means disposed within said structure and coupled to said control means for sensing the temperature within said incinerator structure and for providing said control means with a signal proportional thereto.

3. The system of claim 2 wherein each of said underfire blowers has an inlet and an outlet, the outlet communicating with at least one of said conduits, said blowers further comprising:

shutter means mounted over the inlet of each of said blowers and operably coupled to said control means for restricting the flow of air through said blower responsive to a predetermined Signal from said control means.

4. The system of claim 3 wherein each of said overfire blowers has an inlet externally to said structure and an outlet directed into said incinerator structure said blowers further comprising:

shutter means mounted over the inlet of each of said blowers and operably coupled to said control means for restricting the flow of air through said blowers responsive to a predetermined signal from said control means.

5. The system of claim 4 wherein said vents in the walls of said incinerator structure are disposed in a common horizontal plane above the burner floor and equidistantly spaced therearound, each of said vents being tangentially directed into the interior of said structure.

6. The system of claim 5 further comprising:

first horizontal link means interconnecting the dampers of adjacent vents around a first half of the circumference of said structure for opening and closing said dampers responsive to linear actuation in a horizontal direction;

second horizontal link means interconnecting the dampers of adjacent vents around a second half of the circumference of said structure for opening and closing said dampers responsive to linear actuation in a horizontal direction;

first linear actuator connected to said first link means and operably coupled to said control means for actuating said link means responsive to a predetermined signal from said control means;

second linear actuator connected to said second link means and operably coupled to said control means for actuating said link means responsive to a predetermined signal from said control means.

7. The system of claim 6 wherein the exhaust damper means further comprises:

a horizontal truss member extending across the central portion of the incinerator exhaust outlet; first and second downwardly opening doors hingedly attached to said truss member, said doors movable from an open position wherein they extend vertically from said truss member to a closed position wherein they extend horizontally therefrom and engage the sides of said outlet;

means connected to said doors and operably coupled to said control means for opening and closing said doors responsive to a predetermined signal therefrom.

8. The system of claim 7 wherein said control means includes at least one potentiometric controller.

9. The system of claim 8 wherein said control means includes first and second potentiometric controllers coupled to said first temperature sensing means, said first controller operably coupled to the underfire and overfire blower shutter means and to the vent damper actuators; said second controller operably coupled to said means for opening and closing said exhaust outlet doors.

10. The system of claim 1 further comprising:

recording means mounted externally to said structure for recording the temperature therein; second temperature sensing means extending into the interior of said structure and operably coupled to said recording means for sensing the temperature within said structure and transmitting a signal responsive thereto to said recording means for recording thereon. 

1. An improved draft system for an incinerator structure having a burner floor, walls extending upwardly therefrom, an exhaust outlet in the upper portion thereof, and fuel supply means including a conveyor extending through a port in the upper portion of said incinerator walls and terminating over said floor, said conveyor adapted to drop fuel in a preselected zone on said floor, said structure comprising: a plurality of mutually spaced underfire draft boxes, each of said boxes mounted in the floor of said incinerator, the upper surface of each box forming a grate, said draft boxes being spaced in a predetermined configuration about the conveyor drop zone; a plurality of underfire blowers mounted externally to said incinerator, and separate conduits interconnecting said draft boxes and said blowers, each of said draft boxes separately communicating with the outlet of one of said blowers through one of said conduits; a damper disposed within each of said conduits adjacent said blowers, said dampers adapted to separately control the flow of air from each of said blowers to each of said draft boxes; a plurality of overfire air blowers mounted on the exterior of said structure with outlets extending through the side walls thereof, said blower outlets being tangentially and horizontally directed into the interior of said structure to provide a cyclonic circulation of air currents within said structure; a plurality of mutually spaced vents extending through the walls of said incinerator each of said vents having a damper therein; damper means disposed in the exhaust outlet of said structure for restricting the passage of exhaust gases therethrough; temperature responsive control means operably coupled to said underfire and overfire air blowers, to each vent damper and to said exhaust damper means for permitting only a preselected flow of air into said structure and of exhaust gases from said structure so that when woody materials are consumed in said incinerator structure, the combustion temperature thereof may be maintained within a predetermined range for complete combustion.
 2. The system of claim 1 further comprising first temperature sensing means disposed within said structure and coupled to said control means for sensing the temperature within said incinerator structure and for providing said control means with a signal proportional thereto.
 3. The system of claim 2 wherein each of said underfire blowers has an inlet and an outlet, the outlet communicating with at least one of said conduits, said blowers further comprising: shutter means mounted over the inlet of each of said blowers and operably coupled to said control means for restricting the flow of air through said blower responsive to a predetermined signal from said control means.
 4. The system of claim 3 wherein each of said overfire blowers has an inlet externally to said structure and an outlet directed into said incinerator structure said blowers further comprising: shutter means mounted over the inlet of each of said blowers and operably coupled to said control means for restricting the flow of air through said blowers responsive to a predetermined signal from said control means.
 5. The system of claim 4 wherein said vents in the walls of said incinerator sTructure are disposed in a common horizontal plane above the burner floor and equidistantly spaced therearound, each of said vents being tangentially directed into the interior of said structure.
 6. The system of claim 5 further comprising: first horizontal link means interconnecting the dampers of adjacent vents around a first half of the circumference of said structure for opening and closing said dampers responsive to linear actuation in a horizontal direction; second horizontal link means interconnecting the dampers of adjacent vents around a second half of the circumference of said structure for opening and closing said dampers responsive to linear actuation in a horizontal direction; first linear actuator connected to said first link means and operably coupled to said control means for actuating said link means responsive to a predetermined signal from said control means; second linear actuator connected to said second link means and operably coupled to said control means for actuating said link means responsive to a predetermined signal from said control means.
 7. The system of claim 6 wherein the exhaust damper means further comprises: a horizontal truss member extending across the central portion of the incinerator exhaust outlet; first and second downwardly opening doors hingedly attached to said truss member, said doors movable from an open position wherein they extend vertically from said truss member to a closed position wherein they extend horizontally therefrom and engage the sides of said outlet; means connected to said doors and operably coupled to said control means for opening and closing said doors responsive to a predetermined signal therefrom.
 8. The system of claim 7 wherein said control means includes at least one potentiometric controller.
 9. The system of claim 8 wherein said control means includes first and second potentiometric controllers coupled to said first temperature sensing means, said first controller operably coupled to the underfire and overfire blower shutter means and to the vent damper actuators; said second controller operably coupled to said means for opening and closing said exhaust outlet doors.
 10. The system of claim 1 further comprising: recording means mounted externally to said structure for recording the temperature therein; second temperature sensing means extending into the interior of said structure and operably coupled to said recording means for sensing the temperature within said structure and transmitting a signal responsive thereto to said recording means for recording thereon. 